The chromatographic supports which have been developed hitherto in ion-exchange chromatography are most frequently based on natural polymers, modified in order to bear groups permitting the exchange of cationic proteins (carboxymethyl, sulfopropyl groups) or anionic proteins (aminoethyl, diethylaminoethyl groups). However, these supports are gels which permit use only at low pressure, thereby considerably limiting their use on the industrial scale. In effect, their low mechanical strength limits, or even prohibits, their use in HPLC and, accordingly, their industrial value.
To remedy these drawbacks, supports which, by virtue of their crosslinking, possess good mechanical properties, that is to say good rigidity, have already been sought for these applications. Among the polymers which have thus been proposed, polyacrylamide, trisacrylic polymer, poly(hydroxymethyl methacrylate) and vinyl polymers may be mentioned. However, the chemical modifications which have been performed for the purpose of endowing the base polymers with the character of an ion-exchange support often remain difficult, and the degrees of substitution obtained are generally low.
Thus, supports based on crosslinked polystyrene with a content of the order of 2% of divinylbenzene possess excellent mechanical qualities, but their strongly hydrophobic nature has, to date, limited their use in protein chromatography. In order for such a support to be usable in the exchange chromatography of products of biological origin, it is necessary for it to be heavily substituted with units that are both hydrophilic and ionizable.